Method of coloring magnesium and magnesium alloys by etching



Patented Jan. 15, 1924.

UNITED STATES PATENT OFFICE] FELIX THOMAS, or rarmxronr-on-rnn-mam,GERMANY, assrenoa TO THE FIRM CHEMISCHE FABBIK GBIESHEIM-ELEKTBON,FRANKFORT-ON-THE-MAIN, GEE- MANY, A. COBI'OBATIONDF GERMANY. 4

mnon or cononme naennsrum AND maennsrom annoys Br n'rcnmo.

no Drawing.

To all whom it may concern:

Beit known that Fnmx THOMAS, a citizen of the German Republic, residingat 53 Paul Ehrlichstrasse, Frankfort-on-the-Main, Gerrs many, hasinvented certain new and useful Improvements in the Method of ColoringMagnesium and Magnesium Alloys by- Etching (for which I have'filedapplication in Germany Aug. 26, 1919, application No.

028,289), of which the following is a specification.

This invention relates to a method of coloring magnesium andmagnesiumalloys by etching.

In the following specification and claims the term coloring comprisessuperficially etching the metal in such a way that a small amount of themagnesium metal or magnesium allo is dissolved out and is replaced by ahr of a color differing from that of the metal or metal alloy andconsistin of oxides and metals of the salts cont-aine in the etchingbath.

The only methods hitherto known for mly adherent complex depositApplication filed Augustin, 1921. Serial 1%., 494,9.

other acids, does not efi'ect a continuous liberation of hydrogen, butthat after a very short time, a kmd of passive resistance takes place,the metalbecoming covered with a brass-yellow skin. When heavymetalsalts are also present, this skin adheres and be comes darker incoloration. The shade of the color is influenced by the nature of theheavy metal (copper, zinc, manganese, chromium, iron, cobalt and thelike) as well as by the kind of the alloy for example, the depth of thecoloration in an alloy of magnesium with 3 to8% zinc changes, withincreasing content of zinc and the employment of copper salts, from alight brown tone to a bronze brown.

The colorations which as a rule are between-brass and bronze, may alsobe more finely graduated,'the etching bath remainingthe same, b of otheracids and by modifying the duration of etching. I

'Apart from the aforesaid variegated colorings, a deep black also can beobtained by adding to the bath a considerable excess of coloringmetallic magnesinmnomalloysnoimacid instegl pi the additionnoil hemeavymagnesium containing small amounts of zinc or aluminium, or both thesemetals together,-

know-n under the name of electron metal, by means of the so-calledetching agents are those based ,on the deposition of another metal suchas cobalt followed by baking. The self-evident attempt to apply tomagnesium the methods of metal coloring which aluminium, has not 5 areused for colorin proved very success ul. Also the method 'which is usedfor aluminium, that is to-first provide same with a coating of copper,silver or zinc, and then' to' color with the aid of the 40 methods knownfor these metals'has been recognized to.be too roundabout.

The known etching baths used for colorin metals cannot moreover bedirectly applied to magnesium and its alloys for the reason that theyhave a too powerful acid reaction, and thereby corrode the metal toostrongly, and, at best, only a spongy depos1t of the metal is efiected.

Experiments have nesium and electron metal, good and durable colorationscan be attained in a very Simple manner, by etching. It has been foundthat shown that with "magmetal salt.

According to the kind andjcomposition of the baths and thekind of thealloys to be colored, warm or cold'baths must be used.

The adhesion of the coloring to the metallic base is with most bathsconsiderably inthe addition of small amounts creased by keeping theobject for some time i in an air bath, at a temperature between 100 and150 C., after washing oil the etching liquor, and washing thereafterwith boiling water and drying in the air.

EXAMPLE 1.

3-8% of 217M. H

The object to be colored must be perfectly clean, '(especially free fromfat), and su1t-' ably prepared, and is suspended in a bath which iscomposed as follows:

350 grammes sodium bichromate.

94 grammes copper nitrate.

' 100 cc. chemically pure nitric acid, of 1.36 specific gravity.

9,500 cc. water.

-The temperature of the bath is 90 Cl By frequently moving the objectany gas bubbles'which may adhere are dislodged, and dead corners. ofimpbverished bath liquor are prevented. The alteration of the tone ofthe color is observed by withdrawing the o'bj'ectfor a short time. The

colorin'g'is generally complete in 20 seconds to 3 minutes. The objectis then immediately quickly rinsed in cold running Water, dipped for afew seconds in pure boiling water and dried by rubbing with a softcloth, or placed in an air bath at a temperature in the neighbourhood ofthat of boiling water for a quarter of an hour. To increase the lustreand strengthen the tone, a light greasing with mineral oils is advantaous.

he following examples relate to the coloring of magnesium and magnesiumalloys by means of bath liquors containing salts of manganese and iron.

' EXAMPLE 2.

Horn coloring.

180 grammes sodium bichromate.

133 grammes manganese sulphate crystals.

20 ccm. nitric acid, (specific gravity 1.36).

Water up to 5 litres.

The bath is used cold. The etching takes about 1 minute. Afterthoroughly washing the object can be dried. at once in a stove at100'120 C., or by wiping with a soft cloth.

EXAMPLE 3.

Brass coloring.

pecially adapted for jiolishe'd articles. The etching takes about ha fto one minute. The after treatment is the same as Example 2.

Exam Block etch/mg foreleg/ran metal. 37.5 grammes; sodium bichroinate.

123 grammes nitric acid (specific gravity Water u to 1 litre.

The bat is used eo1 .Thdebjdttserd" dipped into the bath, kept inconstaiitfmove: ment, taken out after a few seconds, and when theadherent liquid of the-bath no longer reacts with'the metal {but notuntil thh}, are thoroughly cleaned with water.

7 The reaction'fis completed when the evolution of sis no longervisible. After drying, which is'eflecterla-very quickly after a shortdipping in boilingwater, the objects are lightly greased or coated"withcolorless spirit varnish or a special" lacquer for electron-metal.

Finally the etched objects can be heated .by heat treatment at, atemperaturqnp-to to a higher temperature (300 to 400 C.) inorder tostill further darken the tone. A dark brown coloration, for example canthereby be transformed into a brownish black.

What I claim and desire to secure by Letters Patent is 1. The method ofcoloring magnesium and magnesium alloys by etching, which comprises thesimultaneous treatment of said chromic acid and a considerable excess oranother acid. a

4. The method of coloring magnesium and magnesium alloys by etching,which comprises the simultaneous treatment of said metal with chromicacid and a solution of a salt of'heavy metal, and the subsequent heattreatment of the colored object. I

5. Themethod of coloring magnesium and magnesium alloys by etching,which comprises the simultaneous treatment of said metal with chromicacid and a solution of a salt of a heavy metal, with the addition ofsmall amounts of another acid, and the subsequentheat treatment of thecolored object.

6. The methodoLprLducing a black color on magnesium and magnesiiu'n'al'loys,. which comprlses the treatment of said metal with chromicacid and a considerable excess o'f another acid, and the subsequentheattreatment of the colored object.

7. The method of colorin magnesium and r. t

magnesium alloys by etching, which comprises the simultaneous treatmenta:

metal with chromic acid, and a-solution. of

a salt of a heavy metal, and the a ent darkening of the shade of'theeoloredo est ut 400 0. r v I 8. The method of coloring magnesium andmagnesium algpys by etching, which comprise'sthe simultaneoustreatmentoi said metal withchromic acid. and a ,so lut ioi1 of a salt ofa heavy metal, with the addition of small amounts of another acid, andte subsequent darkening" of? the shadqof 't 'e colored object by heattreatment ate. temperature up to about 400 9."The method of producing a,black color on ma esium and magnesium alloys,. whieh comprises thetreatment of sa d metal chromic acid and' a considerable excess ofanother acid and the subsequent darkening metal with chromic acid, andcausing said skin to adhere by treatment with a solution of a salt of aheavy metal.

11. The method of producing a brass yellow skin by etching magnesium andmagnesium alloys, which comprises treatin said metal with chromic acid,causing said skin to adhere by treatment with a salt of a heavy metaland influencing the shade of the color by1 the suitable choice of saidheavy metal sa t.

12. The method of coloring magnesium alloys containing zinc by etching,which comprises simultaneously treating said metal with chromic acid, asolution of a salt of a heavy metal,and a zinc salt, and adapting thezinc contents of the coloring bath to the zinc contents of the alloy.

13. The method of coloring magnesium and magnesium alloys by etchingwhich comprises the simultaneous treatment at a temperature above thenormal of said metal with chromic acid and a solution of a salt of a heametal.

14. The method of coloring magnesium alloys containing zinc by etchingwhich con1- prises increasing the contents of zinc in the solution withthe object of altering the depth of the coloration when said alloy issubsequently simultaneously treated with chromic acid and a solution ofcopper salt and a zinc salt.

15. The method of coloring magnesium and magnesium alloys by etchingwhich comprises simultaneously treating said metal with chromic acid anda solution of a salt of a heavy metal and modifying the duration of thetreatment.

16. The method of providing an alloy of magnesium with 3% to 8% of zincwith a brown color which comprises freeing the metal from fat bycleaning, thereupon constantly moving same in a bath containing sodiumbichromate, copper nitrate, nitric acid and water at a temperature ofbetween 90 C. and as soon as the required coloration has been obtainedquickly rinsing the object in cold running water, immersing it in pureboiling water, and drying the object.

17. The method of providing an alloy of magnesium with a horn colorwhich comprises cleaning the metal and constantly moving same in a coldbath comprising sodium bichromate, manganese sulphate, nitric acid andwater, thereupon washing the object in water and drying same in a stoveat a temperature of C.

18.-The method of providing polished magnesium alloys with a brass colorwhich comprises moving the metal in a bath 'containing sodiumbichromate, ferrous nitrate, nitric acid and water and thereupon washingand drying the object.

19. The method of providing electron metal with a black color whichcomprises moving the metal in a bath containing sodium bichromate,nitric acid and water for a few seconds and as soon as the bath liquorno longer reacts with the metal, but not until then, thoroughly cleaningthe metal with water drying the object after dipping in boiling waterand varnishing the object.

In testimony whereof I afiix my signature.

DR. FELIX THOMAS.

